Coated ethylene-polar monomer copolymer substrate

ABSTRACT

THE ADHESION OF COATINGS TO ETHYLENE-POLAR MONOMER COPOLYMER SUBSTRATES IS ENHANCED BY THE USE, AS AN ADHESION PROMOTER, OF VINYL ACETATE POLYMER IN THE FORM OF A PRIMER COAT.

United States Patent Office 3,697,311 Patented Oct. 10, 1972 3,697,311COATED ETHYLENE-POLAR MONOMER COPOLYMER SUBSTRATE John F. Aleckner, Jr.,Bulfalo Grove, 111., assignor to Union Carbide Corporation, New York,N.Y.

No Drawing. Original application Ser. No. 782,719, Dec. 10, 1968.Divided and this application Mar. 31, 1971, Ser. No. 129,941

Int. Cl. B32b 27/08, 27/32 US. Cl. 117-72 6 Claims ABSTRACT OF THEDISCLOSURE The adhesion of coatings to ethylene-polar monomer copolymersubstrates is enhanced by the use, as an adhesion promoter, of vinylacetate polymer in the form of a primer coat.

CROSS REFERENCE TO RELATED APPLICATIONS This patent application is adivision of application Ser. No. 782,719 filed Dec. 10, 1968, now U.S.Pat. No. 3,637,428.

BACKGROUND OF THE INVENTION (1) Field of the invention The inventionrelates to the coating of ethylene-polar monomer copolymer substrates.

(2) Description of the prior art Ethylene-polar monomer copolymers, suchas ethylenevinyl acetate copolymers, have been used for a number ofapplications which require the use of such copolymers in the form of amolded or shaped object. The use of such copolymers for variousapplications, however, has been curtailed due to the fact that thecopolymers are clear materials which, generally, have poor paintabilityproperties. For many applications, plastic substrates must be paintedfor decorative or other purposes. Those in the art, however, have notbeen able to provide, prior to the present invention, a procedurewhereby ethylene-polar monomer copolymers, in general, may be readilypainted with a well-bonded paint. Where any substantial adhesion of apaint to such substrates was obtained a costly or time consumingpretreatment of the surface of the substrate was usually required, suchas by treating the substrate by one or another procedure for oxidizingsuch surfaces such as by a treatment with flame, corona discharge orchromic acid. In many cases, moreover, the attempts to provide coatingsfor many ethylene-polar monomer copolymer substrates only led to theproduction of coatings which would crack and peel from the surface ofthe substrate when the substrate was flexed under actual or simulateduse conditions.

SUMMARY OF THE INVENTION The adhesion of coatings to ethylene-polarmonomer copolymer substrates is enhanced by the use, as an adhesionpromoter, of vinyl acetate polymer.

An object of the present invention is to provide a means for improvingthe adhesion of coatings to ethylene-polar monomer copolymer substrates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It has been found that theadhesion of various paints or other coatings to ethylene-polar monomercopolymer substrates may be greatly enhanced by the utilization, as anadhesion promoter, of vinyl acetate polymer.

THE SUBSTRATE The substrates which are to be coated in accordanceconditions, that is at 25 C. They will contain about 20 to weightpercent of ethylene and about 5 to 80 weight percent of polar monomer.They include all the copolymer materials which are commonly employed forthe fabrication of ethylene-polar monomer copolymer-based molded orshaped articles. Such copolymers include those which have melt indicesof about 0 to and densities of about 0.925 to 0.970.

The term polar monomer is used in the present specification and claimsto denote a substituted a-olefin which readily copolymerizes withethylene and contains a functional group, incorporates a hetero atom,and contributes to a measurable dipole moment. This differentiates fromother a-olefins such as propylene, butylene, hexane and the like whichdo not have hetero atoms nor readily measurable dipole moments.

Illustrative of the polar monomers and mixtures thereof which can becopolymerized with ethylene to form the substrate copolymers which canbe utilized in accordance with the present invention are the following:vinyl and vinylidene halides such as vinyl chloride, vinylidenechloride, vinylidene bromide and the like; vinyl esters such as vinylformate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl2,4-dimethylpentoate, vinyl pelargonate, vinyl stearate, vinyl pivalate,vinyl tert-butylacetate, vinyl chloroacetate, vinyl chloropropionate,vinyl benzoate, vinyl chlorobenzoate, vinyl diethylacetate, vinyl beta,gamma-dimethyl valerate, vinyl thioacetate, vinyl alcohol and the like;acrylic and alpha-alkyl acrylic acids, their salts, their alkyl esters,their amides and their nitriles such as acrylic acid, chloroacrylicacid, methacrylic acid, ethacrylic acid, methyl acrylate, ethylacrylate, butyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate,n-decyl acrylate, lauryl acrylate, hexadecyl acrylate, octadecylacrylate, methyl methacrylate, butyl methacrylate, methyl ethacrylate,ethyl ethacrylate, acrylamide, N-methyl acrylamide, N,N-dimethylacrylamide, methacrylamide, N-methyl methacrylamide, N,N-dimethylmethacrylamide, methyl vinylacetamide, acrylonitrile,chloroacrylonitrile, methacryllonitrile, ethacrylonitrile, and the like;alkyl esters of maleic and fumaric acid such as dimethyl maleate,diethyl maleate and the like; vinyl alkyl esters and ketones such asvinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether,2-chloroethyl vinyl ether, methyl vinyl ketone, ethyl vinyl ketone,isobutyl vinyl ketone and the like; also vinyl pyridine, N-vinylcarbazole, N-vinyl pyrrolidine, ethyl methylene malonate and the like.

Because of the relative ease with which such substrates may be employedin the present invention the preferred copolymers are those of the vinylesters, particularly vinyl acetate, and the acrylic and alpha-alkylacrylic acids and the salts and alkyl esters of such acids. The salts ofthese acids include those formed from cations which are one, two andthree valence metals such as sodium, lithium, potassium, calciummagnesium, aluminum, barium, zinc, zirconium, beryllium, iron, nickel,cobalt, and the like, and nonmetallic cations such as ammonium (NH Inaddition to ethylene and the polar monomers, the substrate copolymersmay also contain minor amounts, i.e., up to about 5 weight percent, ofone or more other monomers which are copolymerizablewith ethylene andthe polar monomers. Such other monomers would include other vinylcompounds, such as other monoolefins, such as propylene, isopropylene,l-butene, isobutylene, hexene, cyclohexene, and the like; polyolefinssuch as butadiene, isoprene, dicyclopentadiene, norbornene, and thelike; vinyl aryls such as styrene, o-methylstyrene, p-methyl styrene,m-methylstyrene, p-phenyl styrene, o-phenyl styrene, m-phenyl styrene,vinyl naphthalene and the like.

3 The term viny means a compound which contains polymerizable ethylenicunsaturation, i.e.,

The substrates which are employed in the present invention need not bepretreated with any mechanical or other pretreating procedures prior tothe use of the adhesion promoters of the present invention.

The ethylene-polar monomer copolymer substrate may be used in all thevarious forms in which such substrates have commonly been employed bythose in the art, such as in the form of solid, porous or foamedstructures. The substrates may also be in any configuration, such asfilm, sheet, strip, rod Orothermolded or shaped configuration.

The substrates may also be in a rigid or plasticized condition. The termrigid means that the substrate contains less than about 5 percent byweight, based on the weight of the ethylene-polar monomer copolymer inthe substrate, of one or more liquid plasticizers. The term plasicizedmeans that. the substrate contains more than such amounts of liquidplasticizers.

In addition to plasticizers, the ethylene-polar monomer copolymersubstrates may contain other adjuvants which are commonly employed withethylene-polar monomer copolymers in the fabrication of molded objects.Such other adjuvants would include impact modifiers, fillers,lubricants, stabilizers, coloring agents, processing aids and the like.The amounts of the adjuvants that are employed are those whichareeffective for the intended purpose.-

Thus, the elfective amount of plasticizer, for example, is aplasticizing amount, that is, an amount of plasticizer which willappreciably increase the flexibility, processability, workabilityand/ordistensibility of the polymer.

Applications for which the ethylene-polar monomer copolymer substratesmight be used when coated in accord ance with the present invention arethe following: functional or decorative items for automobiles such ashead restraints, door knobs, armrests, bezels, trim, and the like; toys;traffic cones; sporting goods, such as decoys and buoys; and furniturecoverings.

THEE ADHESION PROMOTER The adhesion promoter which is used in accordancewith the present invention is a vinyl acetate polymer. This polymer maybe a. homopolymer of vinyl acetate or it may be a copolymer of vinylacetate and one or more other monomers, including ethylene, which may becopolymerizable therewith. Such other monomers would include all thoseenumerated above with respect to the monomers they may be copolymerizedwith ethylene to form the substrate copolymers. The preferred adhesionpromoter copolymers are those which contain about 2 to 77 weight percentof one or more monomers other than vinyl acetate, and the most preferredof such vinyl acetate copolymers are those which contain about 2 to 77weight percent of ethylene and about 23 to 98 weight percent of vinylacetate.

The polymers. which are used as the adhesion promoters in the presentinvention are normally solid at room temperature. They have densities ofabout 0.94 to 1.0.

Both the copolymer which is used as the substrate and the polymer whichis used .as the adhesion promoter may bemade by techniques commonlyknown to those in the polymerization art.

The adhesion promoter polymer of the present invention may be usedeither as a prime coating or paint, or as an, additive in a top coatingor paint in accordance With the teachings of the present invention.

The term coating. or paint as used with respect to the present inventionmeans a coating or paint that may be thinned with a solvent that is asolvent for the vinyl acetate polymers that are used as the adhesionpromoters. Such solvents would include aromatic hydrocarbons, such asbenzene, xylene, toluenev and coal tar naphtha; ketones; such asacetone, methyl ethyl 'ketone and methyl isobutyl ketone; esters, suchas isopropyl acetate and nbutyl acetate; ethers, such as dioxane;chlorinated hydrocarbons, such as dichloroethylene and trichloroethyleneand others, such as mineral spirits (petroleum distillate, B.P. of about300-385 F.).

By the term solvent it is meant an organic liquid which will dissolve atleast 10 weight percent of the vinyl acetate polymer at 60 C. and willretain at least 10' weight percent of the polymer in solution at roomtemperature.

USE OF THE ADHESION PROMOTER IN THE TOP COAT The vinyl acetate polymeradhesion promoter of the present invention may be added directly to atop coating which is to be applied directly to the ethylene-polarmonomer copolymer substrate. When the vinyl acetate polymer adhesionpromoter is used as an additive in a top coat painting or coating, itshould be used in an amount which corresponds to about 10 to 70 percentby weight of the top coat, based on the non-volatile component contentsof the top coat.

THE TOP COATS The top coats which may be employed with the vinyl acetatepolymer adhesion promoter of the present invention include coatingswhich are useful for indoor and outdoor applications and for functionaland decorative purposes. vSuch coatings usually contain one or morevolatile and/or non-volatile vehicles, and one or more pigments orextenders. One or more driers may also be used to accelerate the dryingof the non-volatile vehicles. Plasticizers may also be used in the topcoating as flexibilizers or extenders. The amounts of the components ofthe coatings or paints, other than the adhesion promoter of the presentinvention, are known to those in the art, and they are dictated by theapplication.

The volatile vehicles include all those solvents in which the vinylacetate polymer adhesion promoter is soluble and in which thenon-volatile vehicles may be dissolved or dispersed. The volatilevehicle is usually employed to reduce the viscosity of the non-volatilevehicles to a more easily-handled consistency so as to ease thebrushability of the coating and provide the fluidity and stability whichare needed for ease of mixing. After the application of the top coat tothe substrate, the volatile vehicles are allowed to evaporate, leavingbehind the non-volatile vehicle to bind the pigment particles to eachother and also provide a continuous coating for the substrate.

The non-volatile vehicles include all those commonly employed in thepaint or coating arts which may be dissolved or dispersed in a solventfor vinyl acetate polymer. Such non-volatile vehicles include resinssuch as natural and synthetic rubber; drying oils; rosinand rosinderivatives; synthetic resins such as alkyd resins; polyolefins,including polyethylene, chlorinated polyethylene, sulfonatedpolyethylene, polypropylene and ethylenepropylene copolymers; vinylresins such as polyvinyl fluoride, polyvinylidene fluoride, polyvinylchloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl acetal,polyvinyl butyral and polyvinyl alcohol; cellulosic resins such ascellulose nitrate and cellulose acetate resins; phenolic resins such asphenolformaldehyde resins; urea and melamine resins; polystyrene; epoxyresins; acrylic resins; silicone resins; polycarbonate resinspolysulfone resins; polyaryl ether resins and the like.

The driers that may be used include salts of various metals. The metalsmost frequently used to form the drier salts are cobalt, lead, zinc,manganese and calcium. The salts are usually naphthenates, oleates orresinates.

The pigments or extenders that may be used include lead oxide, Zincoxide, anatase and rutile titanium dioxide, antimony oxide, basiccarbonatewhite lead, basic sulfate white lead, basic silicate whitelead, leaded zinc oxide, zinc sulfide, lithopone, lead tetraphosphate,zirconium oxide, calcium sulfate, silica, carbon black, red iron oxide,yellow iron oxide, red lead, cadmium sulfide, cadmium lithopones,cadmium sulfoselenides, cuprous oxide, raw and burnt umber, manganite,lead chromates, zinc chromate, Zinc tetraoxychromate, chrome greens,chromic oxide, iron blues, cobalt blue, metallic powders of aluminum,copper, bronze, zinc, lead, gold, silver, tin, nickel and stainlesssteel; and various organic dyes and pigments.

USE OF ADHESIVE PROMOTER AS PRIMER The vinyl acetate polymer adhesionpromoter of the present invention may be used in solution as a primercoating to prime coat the surface of the substrate for the reception ofa top coat of another composition. When so used as a primer, the vinylacetate polymer is preferably dissolved in a solvent therefor so as toprovide a solution which will contain at least 10% by weight of thevinyl acetate polymer. The primer coating must also contain, in additionto solvent and the vinyl acetate polymer, at least about 10 weightpercent, based on the non-volatile component contents of the primercoating, of the non-volatile vehicle which is to be employed in the topcoat.

The primer coating may also contain up to about weight percent of one ormore non-volatile plasticizers, based on the non-volatile componentcontents of the primer coating. Such plasticizers would includephosphate esters, such as tricresyl phosphate, cresyl diphenylphosphate, and octyl diphenyl phosphate; phthalate esters, such asdioctyl phthalate, benzyl cyclohexyl phthalate, butylbenzyl phthalate,cresyl benzyl phthalate, di-Z-ethyl hexyl phthalate, butyl phthalylbutyl glycolate and dioctyl phthalate; and epoxy resins, such as butylepoxy stearate, epoxidized soy bean oil and epoxidized peanut oil.

The primer coating may also include other adjuvants to control orfacilitate the application and drying of the primer coating and the topcoating.

The primer coating is usually applied to the substrate so as to providea layer of primer which is about 0.25 to 1 mil thick after the solventis removed therefrom.

When the vinyl acetate polymers are used as adhesion promoters in theform of a primer coating, the top coating which is thereafter applied tothe thus primed substrate need not contain any of the vinyl acetatepolymer adhesion promoter. The top coats which may be employed in thisregard include all those described above.

Both the primer coating and the top coating may be applied by any of thecommonly employed techniques for applying primers and coatings tosubstrates such as dip coating, roller coating, knife coating, slushcoating and spraying.

In preparing the primer or top coat compositions, it is preferable thatthe soluble components of such systems be admixed with the solventcomponents that are to be employed, at elevated temperatures, in orderto dissolve all of such soluble materials therein and then to add theinsoluble components to the resulting solutions. The admixture of allthe components may be accomplished in a homogenous fashion by any of thecommonly employed techniques which are used for this purpose such asball milling, paint milling, pebble milling and roll mixing. The reducedviscosity values were computed by use of the equation:

t, t ct Reduced viscosity= 6 EXAMPLES A In these examples various topcost formulations were employed with an adhesion promoter additive ofthe present invention. These formulations, that is II-II, are clearformulations, but they could be pigmented or extended with one or moreof the pigments or extenders listed above. In preparing the top coatformulations the vinyl acetate polymer which was employed as theadhesion promoter was dissolved in a portion of the solvent system at anelevated temperature of about 60 C. This solution was then added to asolution of the resin in the remaining solvent and placed in a containerand mixed on a can roller for about 10 to 15 minutes. The formulationsthat were employed were the following:

(I) VINYL RESIN BASED FORMULATIONS Component A Weight percent Vinylresin 1 8.55 Ethylene-vinyl acetate copolymer 2 3.60 Toluene 70.75Methyl isobutyl ketone (MIBK) 17.10

100.00 Component B Weight percent Vinyl resin 1 9.0 Ethylene-vinylacetate copolymer 3 5.0 Toluene 70.5 MIBK 15.5

(II) ACRYLIC RES-IN BASED FORMULATIONS Weight percent Acrylic resin 11.713.3 Ethylene-vinyl acetate copolymer 2 4.7 4.0 Toluene 83.6 82.7

(III) ACRYLIC-NITROCELIJULOSE RESIN BASED FORMULATION Weight percentAcrylic resin 11.80 I/ 2 second nitrocellulose resin solution 5 8.55Ethylene-vinyl acetate copolymer 2 5.35 n-Butyl acetate 26.00 Isopropylacetate 9.55 Toluene 26.00 Xylene 12.75

Vinylchloride-vinylacetate-vinyl alcohol terpolymenwhich contains suchmonomers in a 91/3/6% weight ratio and which has a viscosity of 315centipoises as a 20% solids content solution in MIBK.

2 Ethylenevinylacetate copolymer adhesion promoter wh ch contains suchmonomers in a 72/28% weight ratio and which has a density of 0.95 and amelt index of 350.

3 Etltylene-vinylacetlate copolymer adhesion promoter wh ch containssuch monomers in a 67/33% Weight ratio and which has a density of 0.955and a melt index of 20.

4 Methylmethacrylateethyl acrylate copolymer which contains suchmonomers in a 75/25% weight ratio and whi h has a viscosity of 1000-2500centistokes as a 40% solids content solution in toluene.

5 Solution contained, by weight,

(a) 20% second RS nitrocellulose (b) 24% toluene (c) 56% methyl ethylketone These formulations were applied to the following substrates whichwere in the form of solid sheets about 30 to mils thick:

(a) Ethylene-vinylacetate copolymer which contained 82% by weight ofethylene and 18% by weight of vinylacetate and had a density of 0.94 anda melt index of 2.5,

(b) Ethylene-ethyl acrylate copolymer which contained 82% by weight ofethylene and 18% of ethyl acrylate and, had a density of '0.931 and amelt index of 6, and

(c) Ethylene-acrylic acid copolymer which contained 86% by weight ofethylene and 14% by weight of acrylic acid and had a melt index of 5.

The top coatings 'were applied by dip coating or by spraying so as toprovide the substrate, after the removal of the solvents in the topcoating, with a layer of top coat which was of the order of about 0.5 to1.5 mils thick.

The adhesion ofthe coatings to the substrates was evaluated by aflexing. and a cross-hatch test.

In the flexing test the coated substrate was flexed once about 180under'ambient conditions. The flexing did not produce any cracking orpeeling of the paint from the substrate in all cases where the paintcontained the vinyl acetate polymer adhesion promoter of the presentinvention. Where the adhesion promoter was not used in the paint,however, the paints readily cracked under the fiexing test in all casesunder the same test conditions.

In the cross-hatchtest a cross-hatched pattern is cut in the surface ofthe painted sample with a razor blade. A piece of cellophane tape isthen placed over the crosshatched pattern and the tape is then removedin an attempt to lift the coating from the surface. -In all thoseinstances where the cross-hatch test was applied to a paint employingthe vinyl acetate polymer adhesion promoter of the present invention, nopeeling of the paint occurred. However, where the same base paints wereemployed without the adhesion promoter of the present invention and thecoated substrates were subjected to the cross-hatch test, the unmodifiedpaints were readily peeled from the substrates. In all cases thesubstrates were not treated in any fashion prior to the application ofany of the paint formulations thereto.

Afterthe application of the modified or unmodified paints to thesubstrates, the paints were allowed to dry in air at ambienttemperatures of about 25 C. overnight before the commencement of any of.the tests indicated above.

EXAMPLES B This series of examples illustrates the use of a vinylacetate polymer adhesion promoter as an additive in a pigmented topcoating in accordance with the present invention. The top coatformulation used was the following:

Component: Percent by weight (a). 9'1/3/6 weight percent vinyl chloride-This top coat formulation was directly applied to untreated samplesofsubstrates (a) and (b) of Examples A by dip coating so as to providedried coatings having a thickness of about /2 mil. The coatings dry atroom temperature overnight. The dried coatings were subjected to theflexing and cross-hatch tests described in Examples A. The coatings didnot crack or peel under such tests, whereas when the same coating isused, but without the inclusion of the vinyl acetate copolymer adhesionpromoter, the coatings fail these tests.

EXAMPLES C This series of examples illustrates the useof a vinyl acetatepolymer. adhesion promoter in a primer coating,

8 over which a topcoating is applied, in accordance with the presentinvention.

The primer coating had the following composition:

Component: Percent by weight (a) 91/3/6 weight percent vinylchloridevinyl acetate-vinyl alcohol terpolymer of This primer coatingwas directly applied by spraying so as to provide, after drying acoating of about A to /2 mil thickness on untreated samples ofsubstrates a and b t of Examples A. The primer coatings dried at roomtemperature in about 3 to 5 minutes.

After the primer coatings had dried a top coating was directly appliedby spraying so as to provide a dried top coating about one mil thick.The top coating employed had the following composition:

Component: Percent by weight (a) 91/3/6 Weight percent vinylchloridevinyl acetate-vinyl alcohol terpolymer of Examples A 13.5 (b)Dioctyl phthalate 5.0 (c) MI BK 42.5 (d) Toluene 33.5 (e) Xylene 5.5

The top coatings were dried at room temperature over,- night. The driedtop coatings were subjected to the flexing and cross-hatch testsdescribed in Examples A. The top coatings did not crack or peel undersuch tests, whereas when the same top coating is used, without a primercoating containing the vinyl acetate polymer adhesion promoter of thepresent invention, the top coating fails to adhere.

What is claimed is:

1. An ethylene-polar monomer copolymer substrate having a coatingadhered thereto, which comprises:

(a) an ethylene-polar monomer copolymer substrate wherein said copolymercomprises 20 to 95 Weight percent of ethylene and 5 to weight percent ofpolar monomer and wherein said polar monomer is a 'vinyl ester, acrylicacid or alpha-alkyl acrylic acid, or a salt or alkyl ester of suchacids,

(b) a primer coat adhered to and superimposed on said substrate, saidprimer coat consisting essentially of vinyl acetate polymer which iseither a homopolymer of vinyl acetate or a copolymer which consists ofabout 2 to 77 weight percent of ethylene and about 23 to 98 weightpercent of vinyl acetate,

(c) a coating adhered to and superimposed on said primer coat, thecoating being thereby adhered to the substrate, and

said coating being one that may be thinned with an organic solvent forsaid vinyl acetate polymer.

2. A coated substrate as in claim 1 in which the vinyl acetate polymerused in the primer coat is a vinyl acetate homopolymer.

3. A coated substrate as in claim 1 in which the vinyl acetate polymerused in the primer coat is a copolymer of vinyl acetate and ethylene.

4. A coated substrate as in claim 1 in which said polar monomer is vinylacetate.

5. A coated substrate as in claim 1 in which said polar monomer is ethylacrylate.

9 10 6. A coated substrate as in claim 1 in which said polar 3,340,0919/ 1 967 Zweig 117-138.8 E monomer is acrylic acid. 3,427,184 2/ 1969'Mauro et a1. 117138.8 E X 3,442,687 5/1969 Hagan 1l713'8.8 E XReferences Cited UNITED STATES PATENTS 5 3,205,077 9/1965 Hammond117--138.8 E X 3,232,789 2/1966 Pelzek ct E 11776 F, 138.8 E, 138.8 UA,161 UC, 161 UB RALPH HUSAOK, Primary Examiner

